Video optimization, especially for interactive video and audio applications (UC&C VoIP, video telephony, video conference, live-streaming, etc), uses network media services, such as congestion management, network traffic engineering, and network status feedback to allow new rate-adaptive video endpoints to adapt to the network condition effectively. There are two feedback sources: 1) decoder endpoint, and 2) network routers/switches on the RTP path. The endpoint feedback may include up-speed and/or down-speed information via, e.g., RTCP protocol Receiver Report (RR) (lost count, jitter, delay), and RTCP Feedback (FB) extensions, defined in RFC5104. Network feedback may include Explicit Congestion Notification (ECN) and/or Pre-Congestion Notification (PCN) markings. The PCN/ECN is a mechanism for the router to signal the network congestion status; the ratio of PCN/ECN marked packets is used to indicate the congestion severity. Currently the ECN/PCN is widely supported for TCP protocol, while support of UDP protocol is still limited.
Currently, most rate-adaptive encoders rely on the RTCP RR report and FB to adapt the rate. The up-speed rate-adaption is simply a wait-and-see heuristic algorithm that gradually increases the bit-rate if there is no packet loss within an interval. Furthermore, if an RTP packet is lost and a receiver reports it in a RR, the encoder will drop the bit-rate accordingly, depending on the packet loss rate. This mechanism is used after the error (in this case, lost packets) has happened. It would be desirable to adapt the bit-rate before congestion occurs.